Would be well worth a look through the mod called AirQuake's paks.
amgtb.mdl
radpl.mdl
samtb.mdl
Caught my eye.
They could all be used as additional buildings / turrets.
amgtb could be a light assault / nailgun type.
radpl could be used like a tractor beam. Or weapon jammer (Supressor). Or both.
samtb could be used to fire multiple rockets, like a cluster sentry, or the pyro rockets.